The Triassic and Jurassic of East Stara Planina (Bulgaria), Tulcea Zone (North Dobrogea, Romania) and South Crimea (Gorniy Krim, Ukraine)
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Доклади на Българската академия на науките Comptes rendus de l’Acad´emie bulgare des Sciences Tome 59, No 12, 2006 GEOLOGIE Stratigraphie et volcanologie THE TRIASSIC AND JURASSIC OF EAST STARA PLANINA (BULGARIA), TULCEA ZONE (NORTH DOBROGEA, ROMANIA) AND SOUTH CRIMEA (GORNIY KRIM, UKRAINE). ESSAY OF CORRELATION P. Tchoumatchenco, I. Zagorchev, M. Yaneva, K. Budurov, E. Koleva-Rekalova (Submitted on October 18, 2006) Abstract The parautochthonous and allochthonous Triassic and Jurassic rocks in East Stara Planina Mountains (Bulgaria) are relatively deep marine sediments of Tethyan type, deposited in a rift basin (Kotel, East Balkan or Mator Basin). They are re- ferred to the following lithostratigraphic units: (1) Mayadere Formation – irregular alternation of marls, shales, silstones, sandstones and limestones (Olenekian Stage, Spathian Substage); it can be correlated with Tulcea Veche Formation from North Dobrogea similar Triassic rocks being not known in South Crimea; (2) Gyurgenliya Formation – grey, grey-greenish, reddish limestones (Lower Anisian-Lower Carnian); they are correlated with the calcareous-dolomitic Murighiol Formation from North Dobrogea; (3) Glogova Formation – irregular alternation of marls with thin-bedded limestones, calcareous siltstones and peloidal limestones (Upper Carnian-Norian); it can be correlated with the upper part of the Cataloi Formation from North Dobrogea; (4) Sinivir Formation – a flysch-type siliciclastic alternation of sandstones, siltstones and shales to marls containing sideritic concretions (Middle Norian-Toarcian); it is correlated with the Nalbant Formation from North Dobrogea and with the Crimea Formation and the lower member of Eski-Orda Formation from South Crimea; (5) Balaban Formation – thick bedded sandstones (Toarcian?), correlated with the Denis Tepe Formation (North Dobrogea) and the upper member of the Eski-Orda Forma- tion in South Crimea; (6) Kotel Formation (Aalenian-Middle Bathonian?) – black shales with huge olistolites (Wildflysch) that is correlated with the Zebil Formation (North Dobrogea) and Ourgoulya Formation and upper parts of the Ay-Vassil For- mation (South Crimea); the Ourgoulya and Ay-Vassil Formations are separated by the basic effusive rocks of the Upper Bajocian-Lower Bathonian Karadag Formation. The latter has no correlates in North Dobrogea and in East Stara Planina. There are many similarities between the Triassic and the Lower and Middle Jurassic rocks The present study was made under the project NZ-1310/03 of the National Science Fund of the Bulgarian Ministry of Education and Science. 1265 in the three areas, and namely: (a) superposition of comparable rocks; (b) similar lithology of the lithostratigraphic units; (c) high degree of coincidence of the ages of similar lithostratigraphic units. The differences consist in the lack of volcanic activity in East Stara Planina Triassic and Jurassic, whereas volcanics are abundant in South Crimea within the Karadag Formation, and are present as interbeds in the upper member of the Crimea Formation. Key words. Tethyan Triassic, Lower and Middle Jurassic, East Stara Planina – Bulgaria, North Dobrogea – Romania, South Crimea – Ukraine, correlation Introduction. The present paper aims to correlate Triassic and Lower and Middle Jurassic rock units from three well-known areas situated around the Black Sea: East Stara Planina (Balkan) Mountains (Bulgaria), Tulcea Zone of North Dobrogea (Roma- nia) and the South Crimea (Gorniy Krim) of Ukraine (Fig. 1). These rock units have been included in different younger Alpine zones. However, similarities between them allow for correlations and for some palaeogeographic and palaeogeodynamic compar- isons. We will try to expose basic information about the Triassic and the Lower and Middle Jurassic rocks issued from the new results of the study of the rocks in East Stara Planina [1–5] and from the published data – for North Dobrogea [6–8] and South Crimea [9, 10, 19]. Triassic and Lower and Middle Jurassic stratigraphy. East Stara Plan- ina Mountains, Bulgaria. The study of the Triassic and Jurassic rocks in East Stara Planina Mountains started in the beginning of the 20th century [11, 12] when it Fig. 1. Location of the Triassic and Lower and Middle Jurassic in East Stara Planina (Bulgaria), Tulcea Zone (North Dobrogea, Romania) and South Crimea (Gorniy Krim, Ukraine) 1266 P. Tchoumatchenco, I. Zagorchev, M. Yaneva et al. was already demonstrated that a large number of Triassic and Jurassic outcrops repre- sented huge exotic blocks (later named olistolites). This view was entirely or partially shared by later authors [13–15] who introduced the hypothesis that all Triassic and Jurassic rocks in East Stara Planina Mountains represented olistolites into the Upper Cretaceous [15] black shales of the Kotel Formation. Lithostratigraphic subdivisions have been established for the Jurassic [1] and for the Triassic sediments [5]. Recently [16] it has been suggested that in many localities in the Luda Kamchiya Valley the Tri- assic and the Jurassic rocks are in superposition, and the Triassic/Jurassic boundary is situated within the Sinivir Formation. The ages of the rock units have been deter- mined [1, 2, 11–18] on the basis of rich ammonite, bivalve, brachiopod, coral, bryozoan, foraminifer and conodont fauna (for the Triassic), and miospores (for the Jurassic). The Triassic and Jurassic deposits in East Stara Planina Mountains form a thrust sheet sealed by Cenomanian mature conglomerate and sandstone. Two types may be distinguished in respect to their position in the Tethyan sedimentary basin: (a) parautochthonous to allochthonous (basinal Tethyan type), and (b) allochthonous – olistolites, formed predominantly by shelf (Peri-Tethyan) Triassic and Jurassic sedi- ments, and by exotic blocks, coming from the partly destroyed Mator Rift basin. The parautochthonous Tethyan Triassic rocks are subdivided into: Mayadere Formation (Spathian), Gyurgenliya Formation (Lower Anisian–Lower Carnian), and Glogova For- mation (Upper Carnian-Norian to Rhaetian) [5] covered with a transitional boundary by the sediments of Sinivir Formation (now referred to Norian-Toarcian, p.p.), Balaban Formation (Toarcian p.p.) [1], and Kotel Formation [15] (Aalenian-Middle Bathonian?). Mayadere Formation is an irregular alternation of marls, shales, silstones, sand- stones and laminated to slightly convoluted limestones. Gyurgenliya Formation covers the Mayadere Formation with a transitional boundary. It is built up of grey, grey- greenish, reddish or yellowish limestones (usually micritic, with filaments of thin-valved bivalves), in the lower part interbedded with marls, and locally, with silicites. Probably these sediments were accumulated as peri-platform pelagic clays in the upper part of the continental slope. The Glogova Formation is deposited in two environments – on the outer shelf and on the continental slope; in the first case its cover of younger sedi- ments is not preserved (the outcrop represents a big olistolite), and in the second one it is covered by the Sinivir Formation. Glogova Formation is represented by an irregular alternation of marls (dominating in the lower parts) with thin-bedded limestones, silty limestones, calcareous siltstones and peloidal limestones (mainly in the upper parts). The micritic limestones are interbedded by thicker bedded limestones – packstones up to rudstones with bioclasts of crinoids and/or algae and lithoclasts. Probably they are a product of calcareous debris flow. An alternation of limestones (peloidal, silty and silty-sandy, thin-bedded to laminated) and mudstones (ferriferous marls and ferriferous calcareous shales) represents the basinal part of the Glogova Formation The age of the outer shelf sediments is Late Carnian-Norian-Rhaetian, and the sediments deposited on the continental slope (where they are covered by the basinal Sinivir Formation) are of Late Carnian-Middle Norian age. The appearance of the first siliciclastic bed (at Cheshme Bair Hill) coincides with the lower boundary of Sinivir Formation. The Sinivir Formation (c. 500–950 m; Norian – Toarcian p.p.) is a siliciclastic alternation of sandstones to calcareous sandstones, siltstones and shales to marls, with abundant sideritic concretions. In the vicinities of Dropla village it contains pebble conglomer- ates, regarded as a paleo-delta product. In the “Black flysch” (“Schwarzflysch serie”) that has recently [16] been referred to the lower parts of the Sinivir Formation, pres- ence of Norian Halobia has been indicated [3, 4, 14]. The next Balaban Formation is built of thick bedded sandstones (c. 60 m). The formation is referred to the Toarcian by its stratigraphic position. The Kotel Formation (c. 1000 m) has an Aalenian-Middle Bathonian (?) age based upon pollen, spores and dinoflagellate cysts [1, 18]. It is built Compt. rend. Acad. bulg. Sci., 59, No 12, 2006 1267 up of black shales containing numerous Triassic and Jurassic olistolites. In the vicinities of Dropla Village the formation contains also many pebble mudstones due probably also to a delta or a submarine canyon. The younger parts of the Kotel Formation were subsequently eroded. The allochthonous rocks are described as informal lithostratigraphic units (“types”). They originated from the shelf sediments of the Mator Basin, as well as from some rocks from destroyed parts of the Tethyan basin. Upper Triassic rocks of the Orta Kaya type [5] build huge (hectometric) olistolites. The big blocks of Orta Kaya type generally form two distinct packets.